Activation of an electrical consumer

ABSTRACT

A device ( 100 ) for activating an electrical consumer ( 105 ) includes a controllable current source ( 140 ) for providing a control current, a switching unit ( 115 ) for controlling a consumer current as a function of the control current, and a sampling unit ( 145 ) for determining a time delay between an activation of the current source ( 140 ) and the enabling or interruption of the current flow by the switching unit ( 115 ). Furthermore, a processing unit ( 135 ) is provided, which is configured to determine that the current source ( 140 ) is defective if the time delay lies outside a predetermined range.

FIELD OF THE INVENTION

The present invention relates to a technology for activating anelectrical consumer. In particular, the present invention relates to thedetermination of a degradation of a current source in an activation ofthe electrical consumer.

BACKGROUND INFORMATION

A switching unit, which is activated with the aid of a driver circuit,is used to activate an electrical consumer, to enable a current flowbetween the consumer and a predetermined potential. To keep waste heatlow and electromagnetic compatibility high, it is possible to activatethe switching unit for controlling the consumer current using a currentsource instead of using a voltage source. If the current source isactivated, it thus delivers a predetermined control current to theswitching unit, which permits a current flow through the consumer as afunction of the control current. If the switching unit is constructedwith the aid of a bipolar transistor, a current flow may thus becontrollable in an analog manner as a function of the control current;in a specific embodiment having a field-effect transistor, anotherrelationship may exist.

It is possible that the current source degrades on the basis of athermal stress or an aging effect, that is to say, the control currentprovided thereby is excessively large or excessively small. It is then aconcern that the switching unit will be overloaded, so that it may bedamaged, or will not be sufficiently activated, so that it enables thecurrent to move through the consumer excessively slowly or not at all.In a safety-critical application, for example, for activating anelectric motor as a steering aid in a motor vehicle, the activation mustmeet specific reliability and safety requirements. Such requirements arestipulated, for example, in the specification ASIL (automotive safetyintegrity level) corresponding to ISO 26262.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device foractivating an electrical consumer, a method for determining a defect ona current source in the device, and a computer program product, with theaid of which predefined reliability and safety criteria may be met orimproved. The present invention achieves this object with the aid of adevice, a method, and a computer program product having the features ofthe descriptions herein. The further descriptions herein providespecific embodiments.

A device according to the present invention for activating an electricalconsumer includes a controllable current source for providing a controlcurrent, a switching unit for controlling a consumer current as afunction of the control current, and a sampling unit for determining atime delay between the activation of the current source and the enablingor interruption of a current flow by the switching unit. Furthermore, aprocessing unit is provided, which is configured to determine that thecurrent source is defective if the time delay lies outside apredetermined range.

It is thus possible to determine early that the current source degrades,i.e., in particular it operates outside its specification as a result ofslow changes or effects, in that the provided control current isexcessively large or excessively small. For example, if the switchingunit includes a field-effect transistor, initially a gate-sourcecapacitance thus has to be charged during a switching-on procedure, thena Miller capacitance has to be discharged, and finally a gate-sourcecapacitance has to be fully charged to enable complete gating of thefield-effect transistor. If the current source provides an excessivelylarge control current, the field-effect transistor may thus be damagedduring the gating. If the provided control current is excessively small,the gating may take place more slowly or incompletely. In both cases, afunction of a consumer connected to the switching unit may not beensured under certain circumstances. The early determination of adegradation of the current source may therefore contribute to alreadyrecognizing an imminent fault early, in order to output a fault signalor take suitable countermeasures. The reliability and the safety of thedevice may thus be increased.

The direction of the control current is arbitrary; a negative controlcurrent may also be provided so that the current source practicallyoperates as a current sink. The switching unit may alternatively enableor interrupt the current flow as a function of the control current.Hereafter, the case of a current source having a positive controlcurrent for enabling (turning on) a current by way of the control unitis presumed as an example.

In one variant, an external fault may also be determinable with the aidof the device, for example, a parallel connection between a gate of thefield-effect transistor and a ground potential or an incorrectcapacitor, which is connected to the gate.

If the switching unit includes a field-effect transistor, the samplingunit may thus be configured to determine a gate-source voltage of thefield-effect transistor. The degree of the gating or the phase of thegating operation may be read off at the gate-source voltage. Anintegrated driver of the device may already include a sampling orprocessing unit for the gate-source voltage, for example, to detect ashort-circuited switching unit during operation. An already existingdevice may thus be used to determine the control current of the currentsource via the described time delay.

The sampling unit may be configured to determine when the gate-sourcevoltage has exceeded the plateau voltage of the field-effect transistor.If the control current is applied to the field-effect transistor, thegate-source voltage initially does not increase above a specific plateauvoltage, before the Miller capacitance of the field-effect transistor isdischarged. If the gate-source voltage exceeds the plateau voltage,almost the entire current flow is thus already typically enabled by theswitching unit. A sufficiently precise determination of the point intime of the enabling of the current flow may thus be carried out.

If the switching unit includes a field-effect transistor, in analternative specific embodiment, the sampling unit may thus beconfigured to determine a drain-source voltage of the field-effecttransistor. If the drain-source voltage falls below a predeterminedthreshold value, the current flow is thus enabled by the switching unit.If the drain-source voltage exceeds the threshold value, the currentflow is reliably interrupted by the switching unit. The comparison ofthe drain-source voltage to the threshold value may be carried out withthe aid of the processing unit.

In another specific embodiment, a digital counter may be provided forcounting pulses of a clock signal between the activation of the currentsource and the enabling or interruption of the current flow by theswitching unit. The digital counter may already be provided in anintegrated control device, to be able to study chronological sequenceson the control device. The time delay may thus be determined in a simpleand efficient manner.

A method according to the present invention for determining a defect ona current source for providing a control current for a switching unitincludes steps of activating the current source, detecting a time delayuntil a current flow is enabled or interrupted by the switching unit,and determining that the current source is defective if the time delaylies outside a predetermined range.

In particular, it may be determined that the current source provides anexcessively large control current if the time delay is less than thepredetermined range. In a corresponding way, it may be determined thatthe current source provides an excessively small control current if thetime delay is greater than the predetermined range.

A computer program product according to the present invention includes aprogram code arrangement for carrying out the described method when thecomputer program product is run on a processing unit or is stored on acomputer-readable data carrier.

The present invention will be described in greater detail with referenceto the appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit diagram of a device for activating a consumer.

FIG. 2 shows time sequences on a switching unit of the device for FIG.1.

FIG. 3 shows a flow chart of a method for activating the consumer withthe aid of the device from FIG. 1.

DETAILED DESCRIPTION

FIG. 1 shows a circuit diagram of a device 100 for activating a consumer105. Although the provided technology is usable for activating anarbitrary number of switching units 115, the specific embodiment shownin FIG. 1 includes a somewhat more complex example having threehalf-bridges 110, each including two switching units 115, for activatinga consumer 105, which is provided here as a three-phase electric motorin a delta connection. Illustrated switching units 115 are each providedas examples as N-channel field-effect transistors, in particular asMOSFETs. In FIG. 1, first switching units 115, which are shown on top,are each configured to enable a current flow from a first potential 120into consumer 105 and, shown further down, second switching units 115are each configured to enable a current from the consumer 105 to asecond potential 125. A first switching unit 115 is also referred to asa high-side switch and a second switching unit 115 is also referred toas a low-side switch. In other specific embodiments, anotherconfiguration of switching units 115 is provided for enabling a currentthrough consumer 105.

A driver 130, which may be integrated into switching units 115 and/or aprocessing unit 135, is typically provided for activating switchingunits 115. For reasons of clarity, elements of driver 130 are only shownfor one of switching units 115 in FIG. 1; other switching units 115 maybe activated in a corresponding way.

A current source 140 is provided for making available a control currentfor switching unit 115. If current source 140 is activated, inparticular by control of processing unit 135, it thus provides a controlcurrent at switching unit 115, upon which this switching unit enables orinterrupts the described current flow into consumer 105 or out ofconsumer 105. To avoid a short-circuit between potentials 120 and 125,it is to be ensured that both switching units 115 of a half bridge 110do not enable a current flow simultaneously. The activation of bothswitching units 115 is typically carried out by processing unit 135,which has to ensure that the activations are offset in time so that ashort-circuit does not take place. Because switching units 115 turn onor off with a delay upon a corresponding control current, theactivations of current sources 140 may nonetheless be simultaneouslyactive.

A sampling unit 145 is provided to determine a time delay between anactivation of current source 140 and the enabling or interruption of thecurrent flow by switching unit 115. In the illustrated specificembodiment, sampling unit 145 includes a monitoring unit 150 for thegate-source voltage of switching unit 115. In another alternative, thedrain-source voltage of switching unit 115 may instead be monitored withthe aid of monitoring unit 150. Monitoring unit 150 provides the sampledvoltage or a signal when the sampled voltage has exceeded apredetermined threshold value. In the case of the gate-source voltage,this threshold value, as will be explained in greater detail hereafter,may be a plateau voltage of switching unit 115. Furthermore, samplingunit 145 includes a counter 155, which is configured to count pulses ofa clock signal, which are provided by a clock generator 160.

Counter 155 is connected to current source 140 and monitoring unit 150in such a way that the counting of the pulses begins when current source140 is activated and ends when monitoring unit 150 provides a signalwhich indicates that the current flow is enabled or interrupted byswitching unit 115. The counter content of counter 155 is subsequentlyan indication of the time delay between the activation of current source140 and the enabling or interruption of the current flow by switchingunit 115. This delay is typically primarily dependent on an inputcapacitance of switching unit 115, in particular a gate capacitance, ifit is a field-effect transistor, a turning-on threshold of switchingunit 115, and the current strength of the control current provided bycurrent source 140. Because primarily the last-mentioned parameters ofaging and temperature influences on current source 140 are interrupted,while the other parameters typically remain constant, a possibledegradation of current source 140 may be determined on the basis of thedetermined time delay.

FIG. 2 shows time sequences on a switching unit 115 of device 100 fromFIG. 1. A time is plotted in the horizontal direction and a gate-sourcevoltage of a field-effect transistor, which switching unit 115 isimplemented as, is plotted in the vertical direction. A first sequence205 begins when current source 140 applies the correct control currentto switching unit 115. Current source 140 is activated at a point intime T0. From there, the gate-source voltage rises essentially linearlyuntil point in time T3, at which it reaches a plateau voltage 220.During this interval, the gate-source capacitance of switching unit 115is charged. The

Miller capacitance of switching unit 115 is discharged between points intime T3 and T4. The gate-source voltage cannot exceed plateau voltage220 during this time. Subsequently, the gate-source voltage risesfurther, while the gate-source capacitance is completely charged andswitching unit 115 switches through completely.

If the control current of current source 140 is excessively large, asecond sequence 210 thus results. Plateau voltage 220 is already reachedat point in time T1 and left again at point in time T2; the gating takesplace in an accelerated way. This operating mode is stressful forswitching unit 115 and may result in defects, in addition, an emissionof electromagnetic waves may thus be promoted, so that the device doesnot meet the requirements for electromagnetic compatibility (EMC) undercertain circumstances. If the provided control current is excessivelylow, a third sequence 215 thus results. The provided control current isexcessively low here. Plateau voltage 220 is only reached at point intime T5 and cancelled again at point in time T6. Additional stress ofswitching units 115 may thus be caused.

As already described above, it may be determined that switching unit 115enables or interrupts a current flow through consumer 105 when thegate-source voltage exceeds plateau voltage 220. The time delay betweenthe activation of current source 140 and the enabling or interruption ofthe current flow by switching unit 115 is (T4+T0) in first sequence 205,(T2−T0) in second sequence 210, and (T6−T0) in third sequence 215. Withreference to point in time T0, a time range 225 may be specified inwhich the point in time should lie at which the gate-source voltageexceeds plateau voltage 220, to identify the control current provided bycurrent source 140 as correct. If the precise point in time is beforerange 225, the control current is thus excessively high; if it is afterrange 225, it is thus excessively low.

FIG. 3 shows a flow chart of a method 300 for activating consumer 105with the aid of device 100 from FIG. 1. Method 300 begins in a step 305.Subsequently, a step 310, in which counter 155 is started, and a step315, in which current source 140 is activated, may be performedsimultaneously. It is then determined in a step 320 whether switchingunit 115 enables or interrupts the current flow through consumer 105. Ifswitching unit 115 is a field-effect transistor, in a first variant, itmay be determined in a step 325 whether the gate-source voltage exceedsplateau voltage 220. In a second variant, it may be determined in a step330 whether the drain-source voltage is less than a predeterminedthreshold value. If one of the conditions applies, counter 155 is thusstopped in a step 335. Presuming that counter 155 counts upward, it ischecked in a step 340 whether the counter content exceeds an upperlimit. If this is the case, the control current provided by currentsource 140 is excessively small and a degradation of current source 140is determined in a step 345. If the counter content is less than theupper limit, it may thus be determined in a step 350 whether the countercontent is less than a lower limit. If this is the case, the controlcurrent of current source 140 is thus excessively large and adegradation of current source 140 is likewise determined in step 345.Otherwise, the counter content is between the lower limit and the upperlimit and it is determined in a step 355 that current source 140 doesnot degrade, i.e., is not defective.

1-9. (canceled)
 10. A device for activating an electrical consumer,comprising: a controllable current source to provide a control current;a switching unit to control a consumer current as a function of thecontrol current; a sampling unit to determine a time delay between anactivation of the current source and the enabling or interruption of acurrent flow by the switching unit; and a processing unit to determinethat the current source is defective if the time delay is outside apredetermined range.
 11. The device of claim 10, wherein the switchingunit includes a field-effect transistor and the sampling unit isconfigured to determine a gate-source voltage of the field-effecttransistor.
 12. The device of claim 11, wherein the sampling unit isconfigured to determine when the gate-source voltage has exceeded theplateau voltage of the field-effect transistor.
 13. The device of claim10, wherein the switching unit includes a field-effect transistor andthe sampling unit is configured to determine a drain-source voltage ofthe field-effect transistor.
 14. The device of claim 10, furthercomprising: a digital counter to count pulses of a clock signal betweenthe activation of the current source and the enabling or interruption ofthe current flow by the switching unit.
 15. A method for determining adefect on a current source for providing a control current for aswitching unit, the method comprising: activating the current source;detecting a time delay until a current flow is enabled or interrupted bythe switching unit; and determining that the current source is defectiveif the time delay is outside a predetermined range.
 16. The method ofclaim 15, wherein it is determined that the current source provides anexcessively large control current if the time delay is less than thepredetermined range.
 17. The method of claim 15, wherein it isdetermined that the current source provides an excessively small controlcurrent if the time delay is greater than the predetermined range.
 18. Acomputer readable medium having a computer program, which is executableby a processor, comprising: a program code arrangement having programcode for determining a defect on a current source for providing acontrol current for a switching unit, by performing the following:activating the current source; detecting a time delay until a currentflow is enabled or interrupted by the switching unit; and determiningthat the current source is defective if the time delay is outside apredetermined range.